[DIYguy]

Originally Posted by cellsafemode

The valves that are closer to the rear diff are afm valves and they're mechanical on all v6s'. They dont do anything but respond to pressure waves to adjust the sound of the exhaust pulses. They are by their nature an obstruction ...but it's not going to impact performance really, just sound (it's installed and operating on the car when they do all their 0-60 and quarter mile tests that are better than what most people can manage in real life so ...)

I do agree with your basic premise that they were present when specification testing was performed, and therefore if they are not hurting anything why defeat them?
In my case however I discovered the passive flap valves while chasing some annoying buzzing/resonance noises in the exhaust.
I had my wife rev the engine while watching them and saw (and heard) how they operated.
Once they were wired open and hose clamped, the annoying resonance noises disappeared.
Sadly, exhaust "flap" noises are not at all limited to the motorized versions.

BTW, my speed racer days wound down when I sold my 911 some years ago.
I don't really care about 0-60 and quarter mile numbers for my car, and it will never see a race track for as long as I own it.
But I do still care about handling, efficiency, responsiveness and NVH ride comfort.

It's just my thing......